This is so odd that everywhere I have heard about this "bow height" yet in the GM manual they had a plan to confuse me as the bow height is measured from the other way!

Right off the bat I am befuddled as to what an inch one way or the other on this bow is going to do? The GM manual talks about it like it's a frigging piston ring gap or something. If that bow is up or down an inch what the hell would it matter? I could see with a fixed height window, or a glass window. But isn't the height of the window what the whole thing should be based on? What if the repro window isn't perfect, what if the repro top isn't perfect? I am lost on this whole thing being so critical when there is no mention of the top or rear window when this height is discussed.